1. Field of the Invention
The invention relates to a lubricant for use in the shaping of steel at high temperatures, containing a solid lubricant, a binding agent and a thickening agent. 2. Background Art
It is known to use lubricants containing, e.g., graphite, alkylene polymers or copolymers and a dispersing agent or film stabilizer, for the hot forming of metals, especially for the lubrication of the mandrel, in the production of seamless tubes (German Published Patent Specification 2,450,716). Such lubricants must meet a multitude of requirements, especially when they are used in so-called MPM (multiple pipe mills) trains. Thus, it must be possible to apply the lubricant easily, which can be economically accomplished only with the help of an aqueous dispersion, the lubricant must remain behind after removal of the support, in other words, of the water, as a water-resistant, evenly thick film. This film must exhibit a high mechanical stability with homogeneous distribution of the solid lubricant particles up to high temperatures and pressures. An essential share in the fulfillment of these requirements lies with the binding agent. Butadiene and also styrene and styrene with copolymers were mentioned, among others, as binding agents in German Published Patent Specification 2,450,716.
But these known binding agents were unable to meet all of the requirements as such requirements are increasingly made on such lubricants. Butadiene as the binding agent was too soft; styrene on the other hand was unable to form an optimum film even with the usual copolymers. Styrene-butadiene copolymers were also described in European Published Patent Specification 0,164,637 as a component of a high-temperature lubricant. But such formulation requires a considerable amount of an inorganic salt mixture, which, in turn, has adverse effects, e.g., in MPM trains, with regard to a poor water resistance.